1. Field of the Invention
This invention relates generally to an exhaust gas bypass and wastegate valve arrangement for exhaust gas driven turbochargers. More particularly, the present invention provides dual, coaxial shafts for actuation of dual poppet valves on a wastegate for the divided exhaust gas inlets into the turbine housing of the turbocharger.
2. Description of the Related Art
Turbochargers are employed for boosting the pressure level of the intake air for an internal combustion engine. Engine exhaust is provided through an exhaust gas inlet in the turbocharger to spin a turbine wheel which is interconnected via a common shaft to a compressor rotor producing the pressurized charge air. The speed of rotation of the turbine and compressor are dependent on the speed and load of the engine and at high speed, high load operating ranges over pressurization of the charge air may occur. Excessive boost pressure is avoided in turbochargers through the use of a wastegate valve which opens to bypass some portion of the exhaust gas from the exhaust gas inlet around the turbine and directly to the turbine exhaust outlet.
In turbochargers used on engines which can be divided into two banks of cylinders, it has been found highly effective in improving engine and turbocharger performance to maintain separate exhaust gas inlet paths such that separate impulses of the exhaust gas from the two banks of cylinders will be transmitted separately to the turbine. This approach is commonly implemented through the use of a divided exhaust gas inlet. Wastegating of such a divided inlet requires two bypass ports controlled by a dual wastegate valve mechanism.
Dual wastegate valve designs to overcome problems arising from simultaneous opening and closing requirements for both outlet ports have been provided in Japanese Patent Application Laid-Open Publication No. 57-137619, Japanese Utility Model Application Laid-Open Publication No. 62-183033 and U.S. Patent No. 5,046,317, entitled Wastegate Valve for Turbocharger, and having a common assignee with the present application.
It is desirable to provide a wastegate valve mechanism which provides simultaneous opening and closing of dual poppets in an affirmative manner while maintaining the valves in a firmly closed position, when appropriate, to achieve maximum efficiency in transmitting pressure pulses to the turbine. While it is desirable to maintain the individual poppets seated tightly on their respective seats, it is also desirable to accommodate tolerance differences and distortion in the seats, and to absorb pulse loading on the poppets individually to allow reaction as two separate valves.